Rice IPM: Module 4

Module 4. The Third Rule of Rice IPM – Agroecosystem Management

Module Overview

If we were strictly following FAO’s IPM rules this module would only focus on the conservation of natural enemies. However, as we explained in the first module, we have taken a broader interpretation of this rule. In this module we will therefore talk about a wider range of management practices that growers can implement to actively manage the rice agroecosystem. Good agroecosystem management can minimize pest damage from insect pests as well as the many other pests affecting rice. On the following pages we will spend some time on practices that can be employed to actively manage weeds, insects, diseases and non-insect pests like snails, rats and birds. We won’t spend any time on nutrient management as we feel that this has been covered in enough detail in previous lessons.

Lesson 4.1: Weed Management

Effective weed management depends on the integrated use of a range of practices. It has been shown that, even when farmers are using herbicides, these are not nearly as effective (or economical) unless care has been taken in land preparation and the farmer uses water control to manage weeds. No one weed control method is likely to control all weeds, and in the long term this can lead to a build-up of certain species. It is highly recommended to use direct weed control methods (herbicides or hand weeding) with indirect methods (land preparation, flooding, growing a competitive crop).

Weed control in rice, particularly the shift towards herbicide use, is another fairly controversial subject in rice IPM. While the shift is easily understood from the farmer’s perspective (lower costs, unavailability of labor) not everyone agrees that herbicides are the answer. Critics point to environmental and health risks as well as the potential for herbicide resistant weeks.

Lesson 4.2: Insect Pest Management

It was stated early in this course that one of the key concepts in Rice IPM is that insect pests are rarely a problem in a well managed and healthy rice agroecosystem. In most cases, if insect problems develop, it is because something has been done to reduce natural enemy populations. If pests do reach dangerous levels or damage starts to become severe farmers may turn to insecticides.

Key concepts to keep in mind when thinking about managing insect pests is that the best approach is usually to do nothing and that much of the insect damage observed will not affect yields. For example, studies have shown that no yield loss was detected even when 60% of leaves were damaged by whorl maggots. Japonica rice at tillering stage can compensate for as much as 67% of leaffolder damaged leaves.

Lesson 4.3: Natural Enemy Management

Conserving natural enemies is one of the foundations of FAO’s approach. Based on their work in Asia, the members of FAO’s IPM program were convinced that this was the most important limitation of traditional pest control strategies. They also felt that IPM concentrated on insect pests was a useful entry point for a broader approach to IPM.

Numerous studies and experience have since shown that conserving natural enemies is of tremendous importance in the safe and economical management of insect pests and doing so has to be a major component of a grower’s management activities. In simple terms this involves:

Minimizing the application of broad spectrum chemical and natural pesticides

Allowing some pests to live in the field which will serve as food or host for natural enemies

Establishing a diverse cropping system (e.g. mixed cropping)

Including host plants providing food or shelter for natural enemies

Here is a list of some additional specific practices that have shown some success in helping to keep beneficial insect populations high.

Dust suppression: some studies have shown that dusty conditions prevent many predators from being effective as dust interferes with their searching ability. Some of the steps that can be taken to manage dust include leaving groundcover vegetation and the planning of windbreaks. In rural areas oiling or paving roads has been shown to be effective.

Host/prey inoculation: Host/prey insects can be inoculated into a field when the host is scarce.

Alternate hosts/prey: Alternate hosts or prey have also been supplied to natural enemies.

Non-host foods: Pollen and nectar or food sprays are most commonly involved but living sources of non-host foods can be other crops or non-crop plants. Some rice farmers have had success with Water chestnut,Eleocharis sp., can be planted in rice paddies to maintain populations ofTetrastichus schoenobii Ferriere (Hymenoptera: Eulophidae), an important parasite of the rice pest Tryporyza incertulus (Walker).

Intercropping: A summary of intercropping studies (Andow 1986) found that herbivore populations were reduced in 56% of the cases examined. . In general, it is believed that intercropping reduces the advantages an herbivore gains in extensive monocultures and provides alternate resources for natural enemies, e.g. pollen as a food prior to host availability.

Sequential cropping: It is also possible in some cases to plant crops sequentially to gain the advantage of maintaining food sources for natural enemies.

Food sprays: Some growers have had success with spraying fields with a carbohydrate source (sugar or honey) or a protein and carbohydrate source (sugar or honey, plus yeast or casein hydrolyzate). In conservation, the food sprays serve primarily as arrestants, retaining the natural enemies in area, hopefully until the pest population begins to increase.

Refugia: Hedgerows, windbreaks and other areas with perennial vegetation can harbor beneficials species that do not migrate long distances. Trees with grass around them are often best. These are most effective on small acreages because the natural enemies must disperse from the refugia. Thus, its impact will be less important on large farms than on small farms.

Cardboard wrapped trees: Some studies have shown that banding trees with corrugated cardboard make good refugia. Such strips have been found to harbor large numbers of predaceous mites and insects and it was observed that 90% of the residents were entomophagous.

Here are a number of Websites you should visit with more information on conserving natural enemies.

Lesson 4.4: Disease Management

The most effective strategy for disease management in rice involves actions before planting and trying to prevent disease problems from occurring in the first place. Once the rice is planted and infected there is usually not much that can be done. We’ve already talked about the importance of using resistant varieties and planting such varieties is probably the most important action to make. It is also important to be aware that resistance can “break down”. If a grower notices serious infections on a variety that has been disease free for some years it is probably a good idea to switch to another resistant variety.

Infected seed is one of the main ways that diseases are spread and become established in fields and clean and high-quality seed with resistance to locally known diseases should be used as a first step in rice IPM of diseases. Farmers who do not have access to commercial seed sources should follow the practices outlined in the Clean Seed lesson of this course

Diversification (varietal mixture, varietal rotation, varietal deployment, crop rotation) has been shown to be particularly effective in managing some diseases and slowing the capacity of the pathogen to adapt to the resistance of the rice plant. For example, farmers in Yunnan province in China were able to reduce rice blast by 94% by interplanting one row of the incidence of a susceptible glutinous variety every four or six rows of the more resistant commercial variety. Intercropping and diversification work because a more disease-resistant crop, interplanted with a susceptible crop, can act as a physical barrier to the spread of disease spores. Multiple varieties in the field will tend to result in a more diverse array of pathogen populations, possibly resulting in induced resistance and a complex interaction that prevents the dominance of a single virulent strain of the pathogen. It has also been suggested that interplanting changes the microclimate, which may be less favourable to the pathogen.

Once the disease is detected it is important to remove and destroy any diseased plants seen. Pulling and deep burial is one approach used during the cropping season. At harvest, crop residues of infected fields should be plowed under and/or burned. Many farmers have success in breaking a disease cycle by growing a different crop for a season but this may not be feasible for all farmers.

Correct and balanced fertilization has also been shown to help prevent serious disease outbreaks.

Here are the sites that participants should visit for more detailed information on disease management in rice.

Lesson 4.5: Management of Other Pests (Snails, Rats and Birds)

In addition to the pests already covered, there are many more. Rats and other rodents are very destructive in many areas. The golden apple snail is fast becoming a major pest throughout Asia and birds are a common pest. We will try to cover these on the next pages but unfortunately cannot cover some of the more localized pests like crabs, earthworms and crayfish that are also recognized as rice pests for various reasons. If your farmers are facing problems with a pest not covered please try to research the various management options yourself and share what you have learned.

Lesson 4.5.1: Rats

Ask any rice farmer and you will soon learn that rats are one of the most serious pests of rice and also that they are extremely difficult to control. As in the control of insect pests, conservation of natural enemies is perhaps the most efficient approach. Unfortunately, the best natural enemy of rats are snakes and many farmers are reluctant to encourage large snake populations. Another good natural enemy is barn owls and encouraging owl populations has shown some encouraging results in Malaysia.

After natural enemies, a system of using traps-and-barriers with plastic has also achieved good results in rice fields but is not attractive for all farmers for a variety of reasons. Reasons for non-adoption include cost and maintenance requirements and in some countries, the traps and materials are very attractive to thieves and tend to disappear.

Beyond the strategies outlined above, the only examples of successful rat management involve the active participation of an entire community, preferably focused at the early season vegetative stage. Unfortunately organizing communities is a difficult task in itself at any time of the year.

Main community management practices include rat drives, baiting, digging, burning (flamethowers) and sanitation. All are effective if implemented on at least the level of a village. The most effective strategy seems to consist of determining the main species of rat present in order to ensure that baits are appropriate and then developing community-level mapping methods to plan and carry out continuous trapping along feeding routes, fumigation or digging of rat holes, modification of appropriate habitat and establishing early season bait stations using second-generation anticoagulant baits. First generation bait poisons like Zinc phosphide are no longer recommended. For one thing they are very dangerous to humans and livestock and they have been shown to be less effective in rat management because rats tend to eat too little of the poison to cause death. This leads to bait-shyness and poor control.

Here’s one more interesting approach that you might want to evaluate. It is said to be practiced by farmers in Indonesia and is a new twist on the natural enemy approach. Farmers there evidently believe that a “cannibal rat” will keep other rats away from a rice field. Here is their recipe for making a cannibal rat.

Place several rats in a large bucket. Place 0.5 cm water in a large bucket for drinking water. Do not give any food. After a couple days, several of the rats should be missing.

Wait until there is only one rat left in the bucket. Keep water in the bottom for drinking.

When only one rat is left, add one more rat and wait until there is only one rat left.

Release the one remaining cannibal rat. It is claimed that other rats in the area will run away.

Lesson 4.5.2: Snails

The main mollusk pest of rice is the golden apple snail (GAS – Pomacea canaliculata(Lamarck)). This species originated in South America but was introduced into Asia in a misguided attempt to provide additional income and food to poor farmers. It has since found its way into Asia’s rice fields and is a serious and growing problem throughout the region.

What makes this pest particularly difficult to manage is that is has virtually no natural enemies in its new home and is very mobile in its early stages. When small it is easily carried by the flow of irrigation water and spreads rapidly throughout communities.

There are several control measures recommended against the golden apple snail. One recommended management practice for irrigated rice is to place mesh screens at water inlets. This helps to reduce the numbers of snails entering the field with irrigation water. If populations are not too high and labor is not a constraint, many farmers get acceptable levels of control by hand picking or crushing. Farmers can sometimes take advantage of the habit of the Golden Apple Snail to lay eggs on wooden posts inserted in the rice field. When posts are full of egg masses (but before they hatch) simply remove the stakes and destroy the attached eggs. Some other practices include planting older seedlings and periodically draining the field and letting it dry. Draining fields that have several shallow ditches where the snails congregate allows for faster collection and facilitates herding ducks in fields to eat the snails.

Perhaps the most promising approach to snail management involves the use of some unusual natural enemies. Herding ducks through the rice field seems to be particularly effective but some farmers are also having success with fish. Humans make particularly good natural enemies if the incentive is high enough. In Viet Nam, snails provide a valuable and inexpensive source of food for fish farms. Farmers collect, chop, cook and feed so many snails that, in many areas, snail populations are on the decline.

Molluscicides such as metaldehyde should only be used when all else fails.

Lesson 4.5.3: Birds

Birds are known to be very damaging to rice and another difficult pest to manage. In some areas farmers use large nets to catch birds and then either sell them for a profit or eat them themselves. Some farmers in Asia also use fine mesh nets to protect their crops by spreading them over the crop canopy. Many farmers use a variety of methods to scare birds including shouting, throwing dirt clods, sound cannons and scarecrows. Reflective ribbons or used video or cassette tapes strung among the plants is reported to be a particularly effective way to scare birds an some success has been reported with using owl or hawk models. However, these scare tactics are not usually effective for long unless backed up by people moving about the fields and contributing to the effort. Some success has also been reported in destroying nesting habitats but this may not be a very good approach unless farmers are sure that they are only managing the nesting of pest species.